Mobile devices, such as laptop computers, tablet computers, MP3 players, and mobile phones (e.g., cell phones) are becoming increasingly common. Some of these mobile devices have grown more complex over time, incorporating many features, including, for example, MP3 player capabilities, web browsing capabilities, capabilities of personal digital assistants (PDAs) and the like. Mobile devices include charging and/or control jacks into which a charge cable, a power cable, and/or an interface cable to another device (e.g., a desktop computer or home entertainment system), may be plugged so as to charge the battery of the “host device” or transfer data between the host device and the external device. These devices may also include device (e.g., audio) jacks into which a headset or headphones may be plugged. In some cases, the headsets include, in addition to earphones for listening to output of the host device, a microphone to provide input to the host device over a microphone signal line. The later is biased with a DC voltage provided by the host device to operate the microphone.